Productive spring's bottled up (4-5)

I believe the answer is:

well-spent

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'productive' is the definition.
Both the answer and definition are adjectives.
Perhaps there's an association between them I don't understand?

'spring's bottled up' is the wordplay.
'spring's' becomes 'well's' (both can mean a source of water).
'bottled up' becomes 'pent' (I've seen this in another clue. I am not sure about the 'up' bit.).
'wells'+'pent'='WELL-SPENT'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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